Piston



Jan. 26,1926. 1,570,837

. J. E. HOY ET AL PISTON Original Filed March 18,

l'II'I-IIIIIIII'IIII'III'I'III IN VEN TORS .7022 6. ,fi ayma BYJl arnuzn Eesf' A TTORNEYS Patented Jan. 26, 1926.

UNITED STATES PATENT OFFICE.

JOHN E. HOY AND NORMAN A. BEST, OF MIDLAND, MICHIGAN, AS SIGNORS TO THE DOW CHEMICAL COMPANY, OF MIDLAND, MICHIGAN, A CORPORATION OF MICHL GAN.

PISTON.

Application filed March 18, 1924, Serial No. 699,978. Renewed January 22, 1925.

To all whom it may concern:

Be it known that we, JOHN E. HOY and NORMAN A. Binsr, citizens of the United States, and residents of Midland, county of Midland, State of Michigan, have jointly invented a new and useful Improvement in Pistons, of which the following is a specification, the principle of the invention being herein explained and the best mode in which we have contemplated applying that principle, so as to distinguish it from other inventions.

In order to overcome the undue expansion of internal combustion engine pistons formed of light metal alloys, as well as for the sake of the better bearing contact that is obtained between the cast iron cylinder bore and a piston having a skirt likewise of cast iron or of steel, a number of pistons have been designed of composite structure. That is, the bodies of such pistons have been made of a light metal alloy, for -example, one of the numerous magnesium base alloys available for the purpose, and the skirt of the piston has been surrounded by, or encased in, a shell of cast iron or steel, or one or more iron bands, as distinguished from the loosely fitting piston ring, have been attached to the piston skirt. A serious difficulty, however, is encountered whenever it is thus attempted to firmly attach to a light metal piston, with its relatively high oo efiicient of expansion, a band of metal having a lower coefficient of expansion. In other Words, when such a composite piston is subjected to the changes of temperature encountered in' the operation of an internal combustion motor the band will either work loose or the piston skirt be so distorted as to detract seriously from the utility of the de-' vice.

The object of the present invention is the production of a light metal alloy piston, primarily one designed for use in internal combustion engines, to which piston is permanently attached one or more bands of cast iron or steel in such a manner as always to remain firmly in contact with the piston body proper, irrespective of changes in temperature. At the same time any tendency towards distortion of the body of the piston is avoided.

To the accomplishment of the foregoing and related ends, the invention then consists of the means hereinafter fully described and particularly pointed out in the claims; the

annexed drawing and the following description setting forth in detail certain mechanism embodying the invention, such disclosed means constituting, however, but one of various mechanical forms in which the principle of the invention may be used.

In said annexed drawing Fig. 1 is partly a side elevation and partly tofore used in internal combustion engines.

In other words, such piston comprises a more or less cylindrical head portion 1, from which depends a sleeve or skirt portion 2. Such sleeve or skirt portion is formed With oppositely placed inwardly directed bosses 3, which are apertured to receive the wrist pin (not shown) whereby the piston is attached to the connecting rod. Bushings 4 of bronze or equivalent bearing metal are preferably fitted to the apertures in such bosses, as best shown in Fig. 1, and an integral rib 5 between each boss and the head, 1 contributes to the strength of the structure. In order effectually to seal the piston Within the walls of the cylinder in which it works, resilient piston rings (not shown) of familiar construction are seated in annular recesses 6 in the head portion 1, as need not be here explained.

Referring to the specific form of our improved piston, illustrated in Figs. 1 and 2, it will be seen that the skirt portion 2 is substantially surrounded by a shell or band 7. In contradistinction to the light metal alloy whereof the piston proper is composed, as stated above, this shell or band 7 will be made of either cast iron or steel, or other metal of relatively low coefficient of expansion that will corres ond more nearly to the coeflicientof expansion of the metal whereof the engine cylinder iscomposed. Where such shel as in the construction illustrated in Figs. 1 and 2, extends above the wrist pin openings in bosses 3 it will be formed with corresponding openings 8, preferably of somewhat larger diameter, and the lower edge of such shell will furthermore terminate somewhat short of the lower edge of the piston skirt 2. Intermediate of its upper and lower edges, and suitably spaced etween openings 8, a number of other smaller openings 9 are formed in the shell, which are filled in casting with integral projecting portions 10 of the piston skirt.

It will be understood that the metal co nposing the piston proper (head 1 and skirt 2) is cast in a suitable mold, in which such shell or band 7 has been previously placed, the walls of the mold being formed to give the proper contour to the exposed portions of the body and skirt. Such exposed portions as just indicated will include the projections 10 on the skirt, as also the lower edge of the latter which projects in the form I of a flange 11 lying flush with the lower edge of the shell and a similar circular flange 12 that lies within each wrist pin opening 8 in the shell. After casting the cylindrical surface of the composite piston may be machined down and ground or otherwise finished in any approved manner.

The feature of the foregoing construction to which particular attention is directed is the inclination of the laterally contacting surfaces of the lower edge of the shell and of the edges of openings 8 and 9 therein with the opposed surfaces of flanges 11 and 12 and projections 10 on the skirt of the piston. The lines a of contact, as shown in Fig. 2, in every case meet at a point on a central axial line within the piston. Such point, in the particular case illustrated, lies at the center I) of the wrist pin. This point, or other corresponding point, thus selected within the piston will be hereinafter referred to as the neutral expansion point of the structure and, as signified by this term, the result of having the lateral engaging surfaces or the parts in question thus all diverge from such common central point within the piston will be to maintain such surfaces in contact, irrespective of any changes in such parts due to their contraction or expansion, this despite the dinerences in the rate of such contraction or expansion occasioned by the difference in the coeflicients of expansion of the metals when? of the parts are res ectively formed. Accordin ly the band i will at all times remain firmly attached to the piston skirt 2. In the modified construction illustrated in Figs. 3 and 4, aside from the fact that the piston is relatively longer and that the wrist pin bosses 14 are located further down, i. e., at a greater distance from the head 15 of the piston, the general construction is the same as before. However, instead of emflush.with the outer surface of the piston skirt, the openings 18 being filled by projections. 19 on the latter. As before, the

lateral edges of the bands 17 and of the openings 18 therein, together with the complementary edges on the skirt 16 of the piston and the projections 19 of the latter, diverge from a common point on an axial line within the piston. However, we here show separate points 0 and (Z for such contacting edges in the case of such upper and lower bands 17 respectively. It is not necessary, in'other words, in this case that the lines for both bands should diverge from a single point in order to obtain the advantageous results pointed out in describing the first form, i. e., that of Figs. 1 and 2. As shown in Fig. 4, the vertical sides of the projections 19 and the corresponding edges of the openings 18 where intersected on a horizontal plane will lie on strictly radial lines. As a matter of fact, such contacting surfaces in the case of the projections and openings in question will be in the form of conical frustra, either normal or oblique, depending upon whether the corresponding neutral expansion point lies in a plane central with respect to such projections and openings or not. Similarly, the contacting surfaces that bound the edges of the bands will form conical frustra unless, as is permissible, the corresponding neutral expansion point should lie in the same transverse plane with one edge of the band, in which event, of course, that edge will be normal to the cylindrical surface of the piston. In such case, of course, the other edge of the band will be that much more sharply inclined.

The term, light metal alloy, as used herein should be unde3stood to refer not only to aluminum base alloys but also to those in which magnesium is the predominant ingredient. of the composite piston may be referred to in general terms as composed of ferrous metal, cast iron and steel being examples. Any metal part, however, having a different coeflicient of expansion than that of the body of the piston, Whether attached thereto for the purpose hereinbeforestated or for some other, different purpose will be desirably attached in the improved manner characterizing our invention.

It will be understood of course, that the body of the piston or corresponding article may be either cast or forged and that the particular manner of fabrication of the surrounding shell, whether, in other words, it

The shell or band that forms part 1 construction may be secured to a substantial degree by having the contacting edges in 1.0 auestion conform to-surfaces described by be a casting, sta1n ing or forging, does not affect the princip einvolved in our invention.

common point as employed herein does not necessarily imply a strictly geometrical point, since the advantages of ourimproved nes that approximate passing1 through a neutral ex ansion point situate iston as hereinloefore set forth. Finally, it is not essential that all the edges inquestion thus conform, but the principle of our invention may be incorporated 1n part or whole in any composite piston structure, as may be desired.

ther modes of a plying the rinciple of the invention may be em loye instead of the one explained, change being made as regards the mechanism herein disclosed, protion of a vided the, means stated by an of the following claims or the e uiva ent of such ing a relatively high co-eflicient of expansion, of a part surrounding said bod and composed of a metal having a relative y low co-eflicient of expansion, laterally contacting edges of'said body and part converging in 'a general inward direction.

3. In a piston, or like article, the combination witha body composed of a metalhaving a relatively high co-efiicient of ex ansion, of a part surrounding said body an composed of a metal having a relatively {low co-eflicient of expansion, laterally contacting edges of said body and part conforming to surfaces described by .lines passing through an approximately common point lying within said body. 1 Y F It will understood also that the tor-m within the I v 6. In a piston, or like 4. a piston, or like article,' the combina Q 'tion with a body composed of a metal-hav- .ing a relatively high co-eflicient of expan- 'sion; of'a part surrounding saidbod and 'com sed of a metal having a relativ y low co-e cient of expansion, laterally contacting edges .of said body and part conforming to surfaces described b lines passing through a common point in t c axis of said bod 5- 111 a plston, or like article, th c 3 tion'with a body composed of a light metal I alloy; of a part surroundin saidbody andcom osed of a ferrous meta ,l'aterally "conftact ng edges of said body and part conforming to surfaces described by lines p through a common point in theaxisof sai' body.

tion with a body composedpf a metal having a relatively high co-eflicientof expansion artic1e,.the combina- I a of a part surrounding said body and 'comeposed of a metal having a relatively low co-' efficient of expansion, said part bein formed om said body exten and laterallycontacting edges and part conformin to surfaces descri ed by lines passing t rough a with openin s whereinprqections of said bod common point in the axis of said body. 7

7. In a piston,.or like article, the combination with a body composed of a li htmetal' alloy; of a art surrounding said y and composed o a ferrous metal, said part being I formed with openings wherein projections from said bod tacting edges 0 said ingto surfaces described by lines pass througha common. point in the axis ofsgifi body.

8. In a lindrical odyof a light metalialloyshell of ferrous metalsurroundin sa d body and terminatin short of the ower edge thereof, said she beingformed with, a series extend and laterally c'o'nbody and part conform piston, the combination with 0. ey a .of a

of circumferentially spaced 0 nings, whem in proi'ections from said b0 lateral y' contacting edges of said body andshell, including the'lower edgeof said body 'surfaces escribed b" lines passin a; common point in t c axis of sai body.

Signed by us this 13th day of March, 1924.

. 'JOHNE.HOY.

NORMAN a BEST.

y extend, and

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